1. Field of the Invention
The present invention relates to disk drives. More particularly, the present invention relates to a disk drive comprising a pattern dependent overshoot circuit for controlling write current overshoot.
2. Description of the Prior Art
Disk drives employ an inductive write element for writing magnetic transitions on the surface of a magnetizable disk. The digital data stream to be recorded modulates the current applied to the write element, for example, by reversing the direction of the current with each xe2x80x9c1xe2x80x9d bit. During a read operation, the magnetic transitions are detected by a read element (inductive or magnetoresistive), and the resulting read signal demodulated into an estimated data sequence representing the recorded data sequence.
A sufficient amount of current must be applied to the write element during the write ifs operation so that the resulting flux overcomes the coercivity of the disk. Conventional disk drives employ an overshoot circuit which controls the write current overshoot in the write element to ensure that after a present transition the write current reaches a peak value before the next transition. Conventional disk drives also employ a write-precompensation circuit which compensates for non-linearities due to closely spaced transitions referred to as non-linear bit shift.
FIG. 1 shows a prior art disk drive 2 comprising a write driver 4 responsive to write data 6 written to a disk 8 via a head 10. The head 10 is attached to a distal end of an actuator arm 12 which is rotated about a pivot by a voice coil motor in order to position the head 10 radially over the disk 8. The write data 6 modulates the current applied to the head 10 through the write driver 4. For example, a xe2x80x9c0xe2x80x9d bit in the write data 6 may modulate no change in the write current and a xe2x80x9c1xe2x80x9d bit may modulate a reversal in the write current. A current source 14 controls the magnitude of the write current (including a write current overshoot) generated by the write driver 4. The current source 14 is adjusted by an overshoot control register 16 and digital-to-analog converter (DAC) 18 in order to control the amount of write current overshoot. The overshoot control register 16 is loaded with a nominal value by a disk controller 20. The disk controller 20 receives user data from a host to be written to the disk 8, and performs appropriate encoding of the user data (e.g., error correction code (ECC) encoding) to generating write data 22. The write data 22 is shifted through a shift register 24 having taps applied to a pattern detector 26 and to a multiplexer 28. The pattern detector 26 identifies predetermined patterns in the write data 22 which require write-precompensation, and selects the appropriate delayed write data 6 via the multipexer 28. If write-precompensation is unnecessary, the pattern detector 26 selects the non-delayed write data 22 as the write data 6 applied to the write driver 4.
A problem with the prior art disk drive 2 of FIG. 1 is the difficulty in selecting a nominal value for the overshoot control register 16 which ensures sufficient write current overshoot while preventing inter-track interference due to excessive write current overshoot. This problem is exacerbated when a higher coercivity media is employed which exhibits lower media noise but requires more write current overshoot.
There is, therefore, a need to improve control over the write current overshoot in a disk drive to ensure adequate media saturation while preventing inter-track interference due to excessive write current overshoot.
The present invention may be regarded as a disk drive comprising a disk, and a head actuated radially over the disk. A disk controller receives user data from a host computer to be written to the disk, wherein the disk controller generates write data in response to the user data. A write driver generates a write current applied to the head in response to the write data and an overshoot control signal for controlling a write current overshoot in the write current. A pattern detector adjusts the overshoot control signal in response to a predetermined pattern detected in the write data.
In one embodiment, the write driver is implemented in a preamp integrated circuit and the pattern detector is implemented in a read/write channel integrated circuit. In an alternative embodiment, the write driver and pattern detector are implemented in a preamp integrated circuit.
In one embodiment, the pattern detector further generates a delay control signal for delaying the write data in response to the predetermined pattern detected in the write data to compensate for non-linear bit shift.
In one embodiment, the predetermined pattern detected in the write data corresponds to a high frequency pattern in the write current.
In one embodiment, the disk drive comprises an overshoot control register for storing a nominal overshoot value and an offset control register for storing an offset overshoot value. The nominal overshoot value is added to the offset overshoot value to generate the overshoot control signal.
The present invention may also be regarded as a pattern dependent overshoot circuit for controlling write current overshoot in a disk drive. The disk drive comprises a disk, a head actuated radially over the disk, and a disk controller for receiving user data from a host to be written to the disk, the disk controller for generating write data in response to the user data. The pattern dependent overshoot circuit comprises a write driver for generating a write current applied to the head in response to the write data and an overshoot control signal for controlling a write current overshoot in the write current. The pattern dependent overshoot circuit further comprises a pattern detector for adjusting the overshoot control signal in response to a predetermined pattern detected in the write data.
The present invention may also be regarded as a method of writing write data in a disk drive. The disk drive comprises a disk and a head actuated radially over the disk. A write current is modulated in response to the write data, and when a predetermined pattern is detected in the write data a write current overshoot in the write current is adjusted by an overshoot value to generate an adjusted write current. The adjusted write current is applied to the head.
In one embodiment, the method of writing data in a disk drive further comprises the step of delaying the write data by a delay period in response to the predetermined pattern detected in the write data to compensate for non-linear bit shift. In one embodiment, the overshoot value and the delay period are calibrated independently, and in an alternative embodiment they are calibrated dependently.